Diamond films and methods of diamond films

ABSTRACT

The present invention provides films and substrates coated with films that comprise a nano-crystalline diamond matrix that is substantially free of graphite inclusions. The present invention also provides a method of chemical vapor deposition to prepare the films. The method of chemical vapor deposition operates at a DC bias voltage that substantially precludes the formation of a plasma ion capable of causing a region of a nano-crystalline diamond matrix within a forming film to allotrope when the plasma ion collides with the film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/730,967,filed Dec. 9, 2003, which claims the benefit of U.S. ProvisionalApplication No. 60/479,594, filed Jun. 19, 2003, each of which areincorporated herein by reference in their entirety.

FIELD OF INVENTION

The present invention relates to plasma assisted chemical vapordeposition of films and coatings.

BACKGROUND

Carbon exists in several forms (allotropes) which are significantlydifferent in physical and chemical properties. Carbon can exist in thediamond or graphite crystal forms, as well as several amorphous form,such as coal, coke, carbon black, and charcoal. Carbon can also exist inpolymeric forms such as plastic.

Diamond-like carbon (DLC) films comprise a nano-crystalline diamondmatrix with polymeric and/or graphite inclusions. Due in part to theirhardness, wear resistance, capacity for electrical insulation, andinfrared optical properties, DLC films can be used in a wide range ofapplications including protective coatings for a variety of sensitivesurfaces, and infrared anti-reflective coatings on germanium or othersuitable materials.

A range of techniques have been developed to deposit DLC films onsubstrates. For example, radio-frequency (RF) plasma-assisted carbonvapor deposition, sputtering, and ion-beam sputtering have been used.Furthermore, a variety of different carbon-bearing source materials,i.e., solid or gaseous, have also been used in an attempt to provideimproved DLC films. However, these techniques may not provide filmswhich exhibit thermal stability, visible transparency, thermalconductance, and hardness approaching that of diamond.

Desirable properties, such as hardness, scratch and wear resistance,high thermal conductivity, visible transmittance, and electricalinsulation are generally reduced or even destroyed in a DLC film by thepresence of polymeric and/or graphite inclusions. Polymeric inclusionsrepresent defects in the DLC film where carbon-hydrogen bonds exist.Polymeric inclusions can reduce the hardness of a DLC film, reduce heatconduction, and scatter light. Graphite inclusions represent localizedislands or regions in the diamond matrix of a DLC film where carbon isin its graphite crystal structure rather than the more ordered diamondcrystal structure. Graphite inclusions can reduce the visible opticaltransparency, the hardness, the thermal conductivity, the mechanicalshock resistance, and the electrical breakdown threshold of a DLC film.

As a result, there is a need for films comprising a nano-crystallinediamond matrix that is substantially free of graphite inclusions. Thereis also a need for methods for depositing the same onto a substrate suchthat the films may be fabricated at ambient temperature, at low cost,and/or be deposited onto complex substrate shapes.

SUMMARY OF THE INVENTION

The present invention relates to plasma assisted chemical vapordeposition of films and coatings. The films of the present inventioncomprise a nano-crystalline diamond matrix, wherein the nano-crystallinediamond matrix is substantially free of graphite inclusions. The presentinvention also provides a substrate at least partially coated with afilm comprising a nano-crystalline diamond matrix, wherein thenano-crystalline diamond matrix is substantially free of graphiteinclusions.

The present invention also provides a method of depositing a film on asubstrate comprising: (a) providing a plasma chamber containing asubstrate, a radio frequency electrode, and a gas mixture, wherein thegas mixture comprises a hydrocarbon gas having a first partial pressureand a noble gas having a second partial pressure; (b) inducing a plasmain said gas mixture by transmitting a radio frequency from the radiofrequency electrode; (c) producing a DC bias voltage on the radiofrequency electrode; and (d) operating at a DC bias voltage thatsubstantially precludes the formation of a plasma ion capable of causinga region of a nano-crystalline diamond matrix within a forming film toallotrope when the plasma ion collides with the film.

Suitable substrates that may be coated with films of the presentinvention include materials that naturally contain carbon or can easilyreact with carbon. Examples of suitable substrates include plastics,metals that can react to form stable carbides, and other materials thatform stable carbides such as silicon and germanium. Materials whoseperformance may benefit from coating include optical lenses, magneticdisk heads, integrated circuits, various aircraft components such asturbine blades or critical bearings, electronic circuit boards,semiconductor devices, solar energy panels, automobile cylinder sleeves,and medical implants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the chemical vapor depositionapparatus.

FIG. 2 is a wavelength vs. % transmission graph for a 40.5 nm thick filmof the present invention.

FIG. 3 is an infrared transmission of 121.5 nm thick film on glassshowing C-H absorption peaks at 2930 and 2880 cm⁻¹ wave numbers,compared to estimated glass absorption curve.

FIG. 4 is an infrared transmission of 162.0 nm film on glass showing C-Habsorption peaks at 2930 and 2880 cm⁻¹ wave numbers, compared toestimated glass absorption curve.

FIG. 5 is an infrared transmission of 40.5 nm thick film on glassshowing C-H stretching absorption peaks at 2930 and 2880 cm⁻¹ wavenumbers.

FIG. 6A is an atomic force micrograph image of a film of the presentinvention on silicon showing diamond crystallites of size between 10 and50 nanometers.

FIG. 6B is a height profile graph of a cross-section of a film of thepresent invention taken from the atomic force micrograph image of 6A.

FIG. 7A is an atomic force micrograph image of a film of the presentinvention on silicon showing diamond crystallites of size between 10 and50 nanometers.

FIG. 7B is a height profile graph of a cross-section of a film of thepresent invention taken from the atomic force micrograph image of 7A.

DETAILED DESCRIPTION

The present invention provides films and substrates coated therewithwherein the films comprise a nano-crystalline diamond matrix that issubstantially free of graphite inclusions. The present invention alsoprovides methods for depositing such films onto a substrate.

Films comprising a nano-crystalline diamond matrix can be formed in aplasma chamber by feeding radio-frequency (RF) energy to an electrodesystem in the presence of a hydrocarbon gas and a noble gas carrier. Anegative DC voltage is produced on the RF electrode by the action of theRF energy on the plasma. Energetic electrons in the plasma causemolecules of the hydrocarbon gas to disassociate according to modes thatare determined by the type of hydrogen gas. The disassociation of ahydrocarbon gas molecule produces atoms of carbon, hydrogen, and alsofragments of the original molecule. Some of the atoms and fragments areionized. Positively charged carbon atoms are attracted to the negativelycharged RF electrode, and a carbon film is formed. The crystal structureof regions of the film may be in various forms, such as, but not limitedto, graphite, diamond, or the polymeric form.

Previous methods to prepare DLC films provided films comprising anano-crystalline diamond matrix having graphite and/or polymericinclusions. The crystal structure of a nano-crystalline diamond regionof a DLC film is in a lower state of entropy relative to the crystalstructure of a graphite region. Nano-crystalline diamond regions of aforming DLC film can be transformed into graphitic regions if enoughenergy and momentum is provided to the diamond crystallized structure toovercome the barrier to allotropy. For example, the impact of plasmaions with a forming DLC film can cause regions of a nano-crystallinediamond matrix of a DLC film to allotrope to the graphite form.

Films of the present invention are prepared using methods that limit theion bombardment energy in the film forming process to values thatsubstantially preclude the formation of plasma ions capable of collidingwith the forming film and causing a region of a nano-crystalline diamondmatrix within a forming film to allotrope to the graphite form. As aresult, the nano-crystalline diamond matrices of the films of thepresent invention are substantially free of graphite inclusions.

The energy of ion bombardment may be limited by restricting the negativeDC bias present on the electrode to values that preclude the bombardmentof ions having enough energy to cause regions of a nano-crystallinediamond matrix of a film to allotrope to the graphite form. The momentumof the bombarding ions may be partially controlled by employing a noblegas carrier with a mass similar to or below the mass of atomic carbon.Systems using lighter noble gases, such as Ne and He, may allow the useof higher voltages as compared to systems using heavier noble gases,such as Xe, Ar, and Kr, and still substantially preclude the formationof plasma ions capable of causing regions of a nano-crystalline diamondmatrix of a film to allotrope to the graphite form.

As used herein, the term “substantially free of graphite” includes thecomplete absence of graphite and an amount of graphite that is notreadily detectable by ordinary infrared, transmission electronmicroscopy, and atomic force micrograph methods, such as those methodsused to prepare data displayed in FIGS. 2-7. An amount of graphite thatis not readily detectable by ordinary infrared, transmission electronmicroscopy, and atomic force micrograph methods is less than 3 weightpercent of graphite. In an embodiment, the amount of graphite that isnot readily detectable is less than 1 weight percent.

As used herein, substantially precluding the formation of plasma ionscapable of causing regions of a nano-crystalline diamond matrix of afilm to allotrope when the plasma ion collides with the film includesthe complete absence of such ions and an amount of ions capable ofcausing regions of a nano-crystalline diamond matrix of a film toallotrope wherein the nano-crystalline diamond matrix formed issubstantially free of graphite.

Referring now to FIG. 1, a diagram of a chemical vapor deposition (CVD)apparatus 8 is provided that can be used to deposit a film of thepresent invention. The apparatus 8 includes a plasma chamber 10 having athrottle valve 11 which separates the plasma chamber 10 from a vacuumpump not shown. A cathode 19 is mounted to the plasma chamber 10 and isisolated therefrom by a dielectric spacer 20. The cathode 19 can beheated. Nitrogen gas passes through the heater 17, flows through thecathode 19, and exhausts through the tube 16. The RF connection tocathode 19 is between the cathode 19 and the match box 13. A substrate15 is secured to the cathode 19. The cathode 19 is electricallyconnected to a radio frequency source 14 which may be regulated, and theimpedance between the cathode 19 and the radio frequency source 14 isequalized by utilizing match box 13.

The plasma chamber 10 also contains conduits 21 and 22 for introducingvarious gases into the plasma chamber 10. For example, ahydrocarbon-noble gas mixture can be introduced into the reactor chamber10 through conduit 21 while a gas, such as Ar, for cleaning thesubstrate can be introduced through conduit 22.

The hydrocarbon gas useful as a source of carbon cations must be capableof forming a plasma at the reaction conditions employed by the presentprocess. The term hydrocarbon implies that the compound consists ofcarbon and hydrogen atoms. In one embodiment of the invention, asaturated hydrocarbon compound is used. In another embodiment, anunsaturated hydrocarbon compound is used. A saturated hydrocarboncompound contains only carbon single bonds, and an unsaturatedhydrocarbon compound contains carbon double or triple bonds. Suitablehydrocarbons contemplated by the present process include alkanes,alkenes, and alkynes. Mixtures of hydrocarbon gases may also be used.

Alkanes are hydrocarbon compounds that contain only single bonds betweencarbon atoms. Alkanes suitable as a hydrocarbon gas include methane,ethane, propane, and butane.

Alkenes are hydrocarbon compounds that contain a carbon-carbon doublebond. Alkenes suitable as a hydrocarbon gas include ethene, propene, andn-butene.

Alkynes are hydrocarbon compounds that contain a carbon-carbon triplebond. Alkynes suitable as a hydrocarbon gas include acetylene,propylene, 1-butylene, and 2-butylene.

In an embodiment, the hydrocarbon compound comprises acetylene. Inanother embodiment, the hydrocarbon compound comprises ethylene.

In addition to introducing a hydrocarbon gas into the plasma chamber 10,a noble gas is also introduced. Noble gases include xenon (Xe), krypton(Kr), argon (Ar), neon (Ne), and helium (He).

While methods using Ar can provide films substantially free of graphiteinclusions, it is expected that methods using Ne and/or He can provide afilm that is substantially free of any graphite inclusions whileoperating at higher voltages than methods using Ar or heavier noblesgases. As previously discussed, the impact of plasma ions with anano-crystalline diamond matrix of forming film can cause ananocrystalline diamond region to allotrope to graphite. The reducedmomentum of a Ne or He ion colliding with a forming film as compared toheavier noble gas ions at the same voltage can allow greater voltages tobe used and still substantially preclude the formation of plasma ionscapable of causing regions of a nano-crystalline diamond matrix of afilm to allotrope when the plasma ion collides with the film.

Suitable substrates that may be coated with the film of the presentinvention include materials that naturally contain carbon or can easilyreact with carbon. Examples include plastics; metals that can react toform stable carbides; other materials that form stable carbides such assilicon and germanium. Materials whose performance may benefit fromcoating include optical lenses, magnetic disk heads, integratedcircuits, various aircraft components such as turbine blades or criticalbearings, electronic circuit boards; semiconductor devices, solar energypanels, automobile cylinder sleeves, and medical implants.

The method of the present invention can be used to coat substrates thatare incompatible with high temperature methods of the prior art. Thesubstrate and the plasma atmosphere of the plasma chamber can remain atambient temperature during the deposition process.

The substrate to be coated may be any shape or size provided that thesubstrate may be placed in a chamber similar to the plasma chamber 10 ofthe CVD apparatus. Thus, regular or irregular shaped objects having anydimension may be used in the present invention. In an embodiment, asubstrate suitable for coating is one that does not have narrow or deepindentations or one that does not have short radius negative surfaces.

The substrate is mounted on an RF cathode inside the reaction chamber ofthe CVD device. The reaction chamber is then sealed and evacuated untila pressure of about 5×10⁻⁶ to about 1×10⁻⁸ Torr is obtained. A cryogenicpump is suitable to initially evacuate the reaction chamber and toevacuate the reaction chamber during the deposition process. But, acryogenic pump can not remove lighter gases, such as H₂ (created duringthe deposition process), He or Ne. A pump operable to remove H₂, Ne,and/or He gases from the plasma chamber is preferred. One example of apump operable to remove H₂, Ne, and/or He gases is a diffusion pump.Another example of a pump capable of removing H₂, Ne, and He is aturbomolecular pump. A commercially available example of aturbomolecular pump operable to remove H₂, Ne, and/or He gases from theplasma chamber is Model PPU 521C manufactured by Pfeiffer VacuumCompany.

By using a pump operable to remove H₂ from the plasma chamber 10, theamount of polymeric inclusions can be reduced relative to similarmethods using a pump incapable of removing H₂.

The total pressure (the sum of the partial pressures of the hydrocarbonand the noble gases) of the plasma chamber 10 during the depositionprocess is determined by various factors such a desired deposition rate,thickness uniformity, or other process variables. It is expected that asthe ratio of the partial pressure of the noble gas to the partialpressure of the hydrocarbon gas increases, the intrinsic film stresswill change from tensile to compressive stress. By finding the optimumratio of partial pressures, a stress-free film may be formed. In someapplications, a film having compressive stress may be desired. Forexample, the rotors of helicopters could benefit from a coating having acompressive film because the impact of raindrops or sand willmomentarily instill a local tensile stress on the film. Residualcompressive stress in the film can counteract the momentary localtensile stress on the film and reduce damage to the coating and/or therotor.

In other applications a film free of mechanical stress may be desired.For example, films can be used to coat a semiconductor chip forprotection and to conduct away heat. Films used to coat a semiconductorcould be required to have no intrinsic stress (i.e., stress free) sincea film coating a semiconductor having intrinsic stress could damage orchange the electrical properties of the semiconductor.

Relative to a partial pressure ratio that provides a film with nointrinsic stress, a smaller noble gas/hydrocarbon gas ratio will providefilms having tensile stress, and larger ratios will provide films havingcompressive stress. Through experimental determinations known to one ofordinary skill in the art, one may determine the partial pressure ratiothat provides a stress free film. For example, depositing a film atvarious partial pressure ratios on flexible substrates and observing thecurvature of the substrates would provide the necessary information todetermine the partial pressure ratio that provides a stress free film.

The partial pressure ratio of the gases in the plasma chamber may beadjusted by changing the rate of addition of the hydrocarbon and/ornoble gas.

The temperature of the substrate during deposition is limited only bythe thermal stability of the substrate and the desired characteristicsof the film. In an embodiment, the temperature of the substrate is notcontrolled during the deposition process. In another embodiment, thesubstrate is cooled during the deposition process. In anotherembodiment, the substrate is heated during the deposition process.

Depending on the type of substrate used, the material may or may not besubjected to in-situ plasma cleaning prior to depositing the film.

Suitable cleaning techniques employed by the present invention includeH₂, Ar, O₂ and N₂ plasma sputter cleaning techniques. In an embodiment,the plasma sputter etching technique uses the same noble gas used duringthe deposition process. Plasma sputter cleaning is conducted at voltagesabove values that substantially preclude the formation of plasma ionscapable of striking the forming DLC films and the voltage is lowered tosuch values after plasma sputter cleaning the substrate.

The RF frequency of the electrode is operable to form a plasma from themixture of hydrocarbon gas and noble gas. The range of suitable RFfrequencies is from about 0.5 MHz to frequencies in the GHz range. In anembodiment, a suitable RF frequency is from about 0.5 MHz to about 1.0GHz. In another embodiment, the RF frequency is 13.57 MHz.

The hydrocarbon gas and noble gas are introduced into the plasma chamber10 at a flow rate operable to provide a targeted total pressure andpartial pressure ratio. In an embodiment, the flow rate of the gasesinto the plasma chamber 10 is operable to provide a targeted totalpressure that ranges from about 10 millitorr to about 25 millitorr. Inan embodiment, the flow rate of the gases into the plasma chamber is 150sccm for the hydrocarbon and 300 sccm for the noble gas.

The RF power level during the deposition process is adjusted to providea DC bias voltage low enough to substantially preclude the formation ofplasma ions capable of causing a region of a nano-crystalline diamondmatrix within a forming film to allotrope when the plasma ion collideswith the film.

Such a bias voltage for a particular chamber or system can be determinedby lowering the bias voltage progressively through a number ofdepositions. The visible transparency will steadily improve as thenumber of graphitic inclusions declines. Once the general range of biasvoltage is determined, infrared absorption measurements of films of thetype shown in FIGS. 3-5 above can aid in further determining the voltagelevel below which the formation of plasma ions capable of causing aregion of a nano-crystalline diamond matrix within a forming film toallotrope when the plasma ion collides with the film is precluded. FIGS.2-5 are infrared absorption graphs of films of various thicknesses. Theinfrared absorption peaks in these figures between 3200 cm⁻¹, and 2600cm⁻¹ of the films are at 2930 cm⁻¹ and 2880 cm⁻¹ only. One would expectinfrared absorption peaks at 2980 cm⁻¹ and 3100 cm⁻¹ if graphiteinclusions were present in the films in FIGS. 3-5.

In one embodiment where the hydrocarbon gas is acetylene and the noblegas is Ar, the voltage is about 60 volts through out the depositionprocess. In other embodiments where the noble gas is lighter than Ar, itis expected that the bias voltage could be higher and stillsubstantially preclude the formation of plasma ions capable of causing aregion of a nano-crystalline diamond matrix within a forming film toallotrope when the plasma ion collides with the film.

The thickness of a film deposited on a substrate is determined byvarious factors such as the flow rate of hydrocarbon gas into the plasmachamber, the partial pressure of the hydrocarbon gas in the plasmachamber the bias voltage, and the deposition time.

The time necessary to achieve a certain thickness under a certain set ofconditions (system pressure, bias voltage, and hydrocarbon gas partialpressure) can be determined by making a number of samples at the biasvoltage of interest and at various deposit times and measuring thethickness versus the deposit time. In an embodiment of the presentinvention, films having a thickness of between 40 nm and 1000 nm can beprepared.

The surface of the films of the present invention may also approachatomic smoothness. In an embodiment, the average root mean squaresurface roughness of a film is less than 5.00 nm. In another embodiment,the average root mean square surface roughness is less than 2.00 nm. Inanother embodiment, the average root mean square surface roughness isless than 1.50 nm.

Films of the present invention can vary in hardness. One factor that canreduce hardness is the amount of polymeric inclusions in thenano-crystalline diamond matrix of the film. It is expected that as theamount of polymeric inclusions increase the hardness of the filmdecreases. Conversely, it is expected that as the amount of polymericinclusions decrease the hardness of the film increases with the upperlimit being the hardness of pure diamond crystal. In an embodiment, afilm ranges in hardness from 18 GPa to 90 GPa. In another embodiment, afilm has a hardness of at least 60 GPa. In another embodiment, a filmhas a hardness of between 60 GPa and 90 GPa. In another embodiment, afilm has a hardness of between 65 GPa and 90 GPa.

Films of the present invention can vary in thermal stability. One factorthat can reduce thermal stability is the amount of polymeric inclusionsin the nano-crystalline diamond matrix of the film. It is expected thatas the amount of polymeric inclusions increases the thermal stability ofa film decreases. Conversely, it is expect that as the amount of polymerinclusions decreases the thermal stability of a film increases. In anembodiment, a film is thermal stable at 450° C. or higher. In anotherembodiment, a film is thermally stable at 550° C. or higher. In anotherembodiment, a film is thermally stable at 650° C. or higher.

EXAMPLES General Procedure

The substrate, a piece of clear polycarbonate, was attached to the RFelectrode of the CVD apparatus 8. The system was closed, and the plasmachamber 10 was evacuated to a pressure below about 1×10⁻⁶ Torr. Thethrottle valve was adjusted so that the pumping was reduced, and Ar wasintroduced into the plasma chamber 10. The gas rate of flow wasincreased until the system pressure rose to about ½ of the targetpressure of 20 microns.

The RF power was introduced to ignite the plasma system, and the RFlevel (voltage) was adjusted until the self-induced DC bias voltagecaused by the action of the RF plasma rose to the level capable ofplasma sputter cleaning the substrate (300 volts). The substrate wasplasma sputter cleaned for several minutes.

The RF power was reduced until the DC bias voltage was reduced to 60volts. Note, the DC bias level of 60 volts was determined in separateexperiments to identify a bias voltage that substantially precluded theformation of plasma ions capable of causing a region of anano-crystalline diamond matrix within a forming film to allotrope whenthe plasma ion collides with the film.

Acetylene was introduced into the plasma chamber 10, and the flow ratefor acetylene was adjusted until the pressure of the system rose to thetarget value of 20 microns. It was necessary to re-adjust the RF powerwhile introducing acetylene so as to maintain the DC bias voltage at 60volts.

To terminate the deposition, the flow of acetylene was shut off,followed by the RF power and the argon flow. The system high vacuumvalve can then be closed, the system vented to atmospheric pressure, andthe substrate removed.

Example 1

A film having a thickness of 40.5 nm was prepared according to thegeneral procedure above with a deposition time of 15 minutes.

Example 2

A film having a thickness of 81.0 nm was prepared according to thegeneral procedure above with a deposition time of 30 minutes.

Example 3

A film having a thickness of 121.5 nm was prepared according to thegeneral procedure above with a deposition time of 45 minutes.

Example 4

A film having a thickness of 162.0 nm was prepared according to thegeneral procedure above with a deposition time of 60 minutes.

Example 5

A film having a thickness of 486.0 nm was prepared according to thegeneral procedure above with a deposition time of 180 minutes.

Films of the present invention were scanned with transmitted visiblelight, and the results for a film having a thickness of 40.5 nm is shownin FIG. 2. The scan in FIG. 2 was corrected for the glass substrate, andat this thickness the film is not expected to have an appreciablereflection component. The optical density of the film of Example 2 wascalculated and found to vary, as the light varied from the blue to thered end of the spectrum, from a value of 0.089 to 0.022. It was not bedetermined whether the higher optical density at the blue end of thespectrum is due to optical scattering or absorption. Since graphite isabsent in these films, and since the light transmission illustrated inFIG. 2 has the characteristic of scattering, it is held likely thatscattering is the dominant mechanism.

When the C—H stretching frequency is measured in the infrared region,its value is influenced by the characteristics of the C—C bonding in thenano-crystalline diamond matrix. As a result, measurement of the C-Hstretching frequency between 3200 cm⁻¹ and 2800 cm⁻¹ can indicatewhether sp¹, sp², or sp³ bonding between carbons in a nano-crystallinediamond matrix is present, with sp³ carbon bonding associated with thediamond structure.

FIG. 3 shows an infrared absorption spectrum 32 for the film in Example3 and the estimated glass absorption curve 31 in the diamond spectralrange. FIG. 4 shows an infrared absorption spectrum 33 for the film inExample 4 and the estimated glass absorption curve 31 in the diamondspectral range. The C-H stretching peaks at 2930 cm⁻¹ and 2880 cm⁻¹ inFIGS. 3 and 4, show tetragonal carbon bonding.

FIG. 5 is an infrared absorption spectrum for a film of the presentinvention having the non-essential optical background subtracted, andshows the C-H stretching peak at 2930 cm⁻¹. Similar to FIGS. 3 and 4,FIG. 5 shows tetragonal carbon bonding.

The films of the present invention were examined with an atomic forcemicroscope. The atomic force micrographs in FIGS. 6A and 7A show a 2 μm₂section of two films of the present invention. The atomic forcemicrographs show that the two films are polycrystalline with grain sizesfrom about 10 to about 50 nm in diameter. The atomic force micrographsin FIGS. 6A and 7A also show that the two films have an average rootmean square surface roughness of 1.27 nm.

A film of the present invention was examined in scanned visiblereflective light. By analyzing the interference peaks in the reflectedlight, it was found that the index of refraction of the material wasabout 2.28 near the green portion of the spectrum. This number would beexpected to be about 2.4 if little or no hydrogen were incorporated inthe film.

FIGS. 6B and 7B show the height profile of a cross-section of a 2 μm²section of two films of the present invention. The height profiles inFIGS. 6B and 7B show that the difference between peaks and troughs onthe surface of the two films can be less than 80 angstroms (8.0 nm).

The films of Examples 2-5 were found to be insulating, at least at lowvoltages. The electrical breakdown threshold was not determined, but itis expected that it would be higher than normal DLC films because thefilms of the present invention are substantially free of graphiteinclusions.

The substantial freedom of graphite inclusion in the films wasestablished by the infrared scans shown in FIGS. 3-5. In addition, thetunneling electron microscopy (TEM) pattern for the films of Examples2-5 was diffuse circles, and the radius of these circles most closelyfit the reflection planes of diamond crystallites. The diffuse nature ofthe TEM image was due to the small diamond grain size, and the polymericcontent of the films probably appeared on this image as a generalbackground. The diffuse circles more closely correlated with diamondthan graphite. Furthermore, if graphite inclusions were a majorcomponent of the films, it would be expected that “mounds” or “bumps”would be present on the surface of the films since growth of graphitecrystallites would be thermodynamically favored over growth of diamondcrystallites. As discussed above, the atomic force microscope image(FIGS. 6A, 6B, 7A, and 7B) do not show these “mounds” or “bumps”. Thesemeasurements tend to support the infrared scans and indicate the filmsare substantially free of graphite inclusions.

While various embodiments have been described in detail and by way ofillustration, it will be understood that various modifications andsubstitutions may be made in the described embodiments without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A method of depositing a film on a substrate comprising the steps of:(a) providing a plasma chamber containing a substrate, a radio frequencyelectrode, and a gas mixture, wherein the gas mixture comprises ahydrocarbon gas having a first partial pressure and a noble gas having asecond partial pressure; (b) inducing a plasma in said gas mixture bytransmitting a radio frequency from the radio frequency electrode; (c)producing a DC bias voltage on the radio frequency electrode; and (d)operating at a DC bias voltage that substantially precludes theformation of a plasma ion capable of causing a region of anano-crystalline diamond matrix within a forming film to allotrope whenthe plasma ion collides with the film.
 2. The method of claim 1, whereinsaid noble gas comprises helium or neon.
 3. The method of claim 1,wherein said hydrocarbon gas comprises ethylene.
 4. The method of claim1, wherein said radio frequency is between 0.5 MHz and 1 GHz.
 5. Themethod of claim 1, wherein said DC bias voltage is less than or equal to60 volts.
 6. The method of claim 1, wherein the film produced comprisesa nano-crystalline diamond matrix, wherein the nano-crystalline diamondmatrix is substantially free of graphite inclusions.
 7. The method ofclaim 1, wherein the film produced comprises a nano-crystalline diamondmatrix, wherein the infrared absorption peaks between 3200 cm⁻¹ and 2800cm⁻¹ of the nano-crystalline diamond matrix are at 2930 cm⁻¹ and 2880cm⁻¹ only.
 8. The method of claim 1, wherein the film produced comprisesa nano-crystalline diamond matrix, wherein the nano-crystalline diamondmatrix has no infrared absorption peaks at 2980 cm⁻¹ and 3100⁻¹.
 9. Themethod of claim 1, wherein the film produced comprises anano-crystalline diamond matrix, wherein the nano-crystalline diamondmatrix has a hardness of at least 60 GPa.
 10. The method of claim 1,wherein the film produced comprises a nano-crystalline diamond matrix,wherein the nano-crystalline diamond matrix is thermally stable at 450°C. or higher.
 11. The method of claim 1, wherein the ratio of the firstpartial pressure to the second partial pressure produces a film free ofmechanical stress.
 12. The method of claim 1, wherein the ratio of thefirst partial pressure to the second partial pressure produces a filmhaving compressive stress.
 13. The method of claim 1, wherein the ratioof the first partial pressure to the second partial pressure produces afilm having tensile stress.
 14. The method of claim 1, wherein the filmproduced has an average root mean square surface roughness of less than5.00 nm.
 15. A method of forming a film comprising the steps of: (a)providing a plasma chamber, a radio frequency electrode, and a gasmixture, wherein the gas mixture comprises a hydrocarbon gas having afirst partial pressure and a noble gas having a second partial pressure;(b) inducing a plasma in said gas mixture by transmitting a radiofrequency from the radio frequency electrode; (c) producing a DC biasvoltage on the radio frequency electrode; and (d) operating at a DC biasvoltage that substantially precludes the formation of a plasma ioncapable of causing a region of a nano-crystalline diamond matrix withina forming film to allotrope when the plasma ion collides with the film.16. The method of claim 15, wherein said noble gas comprises helium orneon.
 17. The method of claim 15, wherein said hydrocarbon gas comprisesethylene.
 18. The method of claim 15, wherein said radio frequency isbetween 0.5 MHz and 1 GHz.
 19. The method of claim 1, wherein said DCbias voltage is less than or equal to 60 volts.
 20. The method of claim15, wherein the film produced comprises a nano-crystalline diamondmatrix, wherein the nano-crystalline diamond matrix is substantiallyfree of graphite inclusions.